Nitric acid oxidation of hydrocarbons



May 7, I957 G. P. BROWN, JR, ETAL NITRIC ACID OXIDATION OF HYDROCARBONS Filed Aug. 26, 1953 IN V EN TOR5. Geo/ye Para): J 1

Norman M 41740.

United States 2,791,598 'NITRIC ACID OXIDATION'OF- HYDROCARBONS George P. Brown, 'Jr., WestDerTownship, Allegheny County, Edgar I. Crowley, Pittsburgh, and Norman W. Franks, Penn Township, Allegheny County, Pa., assignors to Gulf Research & Development Company, Pittsburgh, Pa., a corporation of Delaware Application August 26, 1953, Serial No. 376,664 8 Claims. (Cl. 260-452) This invention relates to oxidation processes for con verting saturated aliphatic hydrocarbons to organic acids and more particularly to oxidation processes for converting saturated aliphatic hydrocarbons to dibasic acids.

Oxidation of hydrocarbons to produce dibasic acids is known in the art. Thus, it has been shown, as in U. S. Patent No. 2,452,741 to Fleming, thatcyclorparaflins can be oxidized in air and with nitric acid in a two-stage process to produce dibasic acids. It has not been shown, however, how such process can be carried out to produce high yields of dibasic acids while maintaining the amounts 10f nitric acid at a It is not apparent from such process that the degree of oxidation'inair in the first stage is important or critical nor that the specific manner-in which the reaction with nitric acid-in'the second stage takes place can aid in cutting down-on the amount of nitric acid needed in the second stage. MorelOVl', it is notapparent from such process that saturated aliphatic hydrocarbons can be similarly treated to obtain commercial use, the amount of nitric acid necessary to obtain a high yield of dibasic acids is so large as to make the process commercially unattractive.

We have found that the amount of nitric acid needed to produce a high yield of dibasic acids inthe nitric acid oxidation ofs aturated aliphatic hydrocarbons can be snbstantially reduced and the process made commercially iattractiveby subjecting a saturated aliphatic hydrocarbon to oxidation with air or other oxygen containing gas, i. e., a gas containing free oxygen, for a time suflicient to obtain an oxidation product having a saponifi'cation number above about 100, and preferablybetween about 150 and about 450, separating from said oxidation product a fraction having a saponification number higher than said oxidation product and a fraction having a saponification number lower than said oxidation product, and thereafter subjecting said fraction havinga saponification-number higher than said oxidation product to further oxidation at an elevated temperature with nitric'acid having a concentration above about 50, and preferably above about 60 percent, for a time suificient to obtain substantial amounts of dibasic acids while admixing with the gaseous mixture comprising nitrogen oxides formed duringthe nitric acid reaction stage of the process an'oxygen-"containiug gas in amounts and for a time sufficient to regenerate said nitrogen oxides, and employing the products resulting from said regeneration in said nitric acid reaction.

Oxidation of saturated aliphatic hydrocarbons in the ate i Patented May 7, 1957 2 first stage of ourprocess can be conducted satisfactoril either "at atmospheric or elevated pressures. While 0x1- dation ofsaturated aliphatic hydrocarbons in the first "stage can be conducted'at'a'temperature of about C. 'to'about 400 C.,we have found'that'to facilitateoxr 'dation'in the firststag'e,the oxidation'is preferably conducted at 'a'temperature of about C. to about C. The amount of air necessary to obtain the airoxidized product is not critical and can vary from about 2.5 grams to about 10.0 "grams'per gram of a1r-ox1d1zed product obtained. If "oxygen-is used, about 0.5 gram'to about 2.0 grams per gram of air-oxidized product is sufficient.

In-the second stage of our process the oxidized product having 'a-saponification number of at least about 100 obtained'from the first stage is separated 'into'a fraction of lower saponification number anda traction of higher fractionation is preferably accomplished in accordance with our invention by solvent extraction. Theoxidized product-from the first stage'is heated with a solvent at atemp'eratureof about 25C. to about 1 10 'C., and preferably between about '50'C.'to about 60 C., to dissolve the product, and the solution is'then chilled until 'a raiiinatephase separates from a solvent .phase. The rafiinate'phase has the lower saponification number, while the solvent phase has the higher sap onification number. The two layers which are formed are separated and the solvent is stripped from the soluble product, after which the soluble product-is subjected to nitric acid oxidation. The rafiinate phase, having a lower saponification number, can be recy'cledto the first stage-of theprocess. Any solvent which will effect thedesired fractionation can be employed. Good resultscan be obtained withalcohols and ketones, especially C5 and lower aliphatic alcohols and Csand lowerketoneaexamples of which are methanol, ethanol, isopropanol, l-butanoLl-pentanol, acetone, methyl ethyl 'kotone, diethyl ketone, etc. Especially'good results have been obtained with methanol. The ratio of solvent tiooxidation' product obtained in the first stage is not critical'and can be varied over a-wide range, from 0.5 :1 to-about 10:1, with a ratio of about 2.5 :1 being preferred. Any extraction-temperature which will separate a fraction of higher saponifioation number from a fraction of lower saponification number asdefin'ed above from the oxidized product obtainedfrorn the first stage as a separate phase can be employed. A- temperature of about 50 C. to about -20 C. can be employed, with a temperature of abodt-40 C. to Iabout--10 C. being preferred. Especially good results have been obtained at an extraction temperature of about 20 C.

Fractionation of the oxidized product obtained .in the first stage can also be effected by chromatographic separation on such'adsorbent-s as silica gel, bauxite, etc. For those charge stocks for which the unreacted or slightly reacted material is siifficiently volatile, the separation can be effected by distillatio During the oxidation of the air-oxidized. products -of saturated aliphatic hydrocarbonswith' nitric acid, the acid breaks down to form N02, NO, N20, nitrogen and some water. Additionalf'water is present in the nitric acid reaction zone as the "result of the oxidation of'the air-oxidized products of saturated aliphatic hydrocarbons and, of course, since an aqueous solutionof nitric acid is employed, some water is introduced into the nitric acid reaction zone with the acid. N02 dimerizes to form;

,r.....i A

s V 3 N204, which is in equilibrium with N02. N02, as well In addition, in the absence of substantial amounts of oxygen in the nitric acid reactor, N formed will react with N02 to form N203, which is also believed to be an excellent oxidizing agent for air-oxidized products of saturated aliphatic hydrocarbons. At the same time, N02 and N203 will react with the water present toform nitrous as well as nitric acid, both of which are believed to be excellent oxidizing agents for the purpose of this invention. In this way, by utilizing N02, N0, water, other nitrogen oxides and nitrogen acids formed during the process as oxidants in the third stage of our process, the amount of nitric acid necessary in the third stage of our process for converting air-oxidized products of saturated aliphatic hydrocarbons to dibasic acids is substantially reduced.

, We have additionally discovered that some of the nitrogen oxides formed during the third stage of the process can be regenerated to higher oxides of nitrogen, and these higher oxides, as well as nitrous and nitric acids formed therefrom, can be employed as oxidants in the third stage of the process. We have found that the :amount of air or other oxygen-containing gas, i. e. a gas containing free oxygen, necessary to regenerate the nitrogen oxides is not critical, although we prefer to use more than the theoretical amount to insure adequate regeneration. For example, we have found that 520 grams of air or 75 grams of oxygen per 100 grams of air-oxidized products. of saturated aliphatic hydrocarbons and 500 grams of 70 percent nitric acid have been sufficient for purposes of regeneration. Regeneration can be conducted in the nitric acid reactor itself or in a separate regenerator.

In the event regeneration is conducted in the nitric acid reactor, air or other oxygen-containing gas is introduced into the reactor. N02 formed during the process remains unaffected by the presence of oxygen but NO preferentially reacts with oxygen rather than with N02 to form N02. N02 in the reactor will combine with water to form nitric acid and this acid, as well as free N02, is present in the third stage of our process.

If the regeneration is conducted in a separate regenerator, the nitrogen oxides formed are removed from the nitric acid reactor and passed to a separate regenerator. Air or other oxygen-containing gas is also passed to the regenerator. As stated, with no substantial amounts of oxygen in the nitric acid reactor, N0, N02, as well as N203, are formed and these are passed to the regenerator. N02 remains unaifected by the presence of oxygen but NO and N203 are regenerated by the oxygen to N02. The N02 already present, as well as the N02 formed in the regenerator, is condensed therein and recycled to the nitric acid reactor where the N02 reacts with the airoxidized products of saturated aliphatic hydrocarbons as such or is converted by reaction with water to nitric acid. In the regenerator the N02 can combine with water to form nitric acid which is recycled to the nitric acid reactor.

While the amount of nitric acid employed in the nitric acid reaction zone is not critical and may be varied over a wide range, provided sufficient acid is present for the desired oxidation, we have found that charging about 2.5 to about 20 parts of aqueous nitric acid per part of the fraction having the higher saponification number, obtained in the second stage of the process, to the nitric acid reaction zone is sufficient to obtain the desired dibasic acids.

The pressure in the nitric acid reaction zone is similarly not critical and can be varied over a wide range,

. nets of saturated aliphatic hydrocarbon in the nitric acid .reactor.

from about atmospheric to about 1,000 pounds per square inch. We prefer, however, to operate at elevated pressures to facilitate precipitation and condensation of the nitrogen oxides. For best results, we prefer to operate at a temperature of about 50 C. to about 150 C., preferably about 75 C. to about C., in the nitric acid reaction zone. The residence time for the saturated aliphatic hydrocarbons in the nitric acid reaction zone necessary to obtain substantial amounts of dibasic acids varies inversely with temperature. For example, about the same amount of reaction is obtained in a period of about 30 hours at about 75 C. as is obtained in less than about two hours at about 130 C. The reaction can be carried out at a constant temperature or the temperature can be varied with time. For example, the reaction can be started out at a low temperature, say 50' C., and the temperature gradually raised to a selected maximum temperature and the reaction can be discontinued when the maximum temperature is reached or the reaction can be maintained at the selected maximum temperature for the desired length of time.

Saturated aliphatic hydrocarbons boiling above about 250 F. and having about eight or more carbon atoms or mixtures thereof can be employed as charge stock for the production of dibasic acids in accordance with our process, although, for ease of operation, we prefer to employ saturated aliphatic hydrocarbons having from about 10 to about 40 carbon atoms. Included among the saturated aliphatic hydrocarbons which can be employed in our process are petroleum waxes, paratiinic oils, foots oil, oils and waxes obtained from the Fischer- Tropsch process, n-octane, decane, cetane, etc. While we prefer to employ charge stocks consisting of saturated aliphatic hydrocarbons, we can also employ charge stocks which are predominantly saturated aliphatic hydrocarbons and which can contain cycloparaflins. Such charge stocks can be prepared from a variety of types of crude oils. When the crude oil is essentially paratiinic, the charge may be recovered by distillation but where the crude oil is of a mixed type, various combinations of treatments can be employed to obtain the charge, such as distillation and solvent extraction, distillation and crystallization, or chromatographic separation.

A method of carrying out our invention employing a first stage air oxidation, a second stage extraction involving the use of methanol, and a third stage nitric acid oxidation, wherein the third stage of the process is conducted in a closed container and the nitrogen oxides formed therein are regenerated in a separate regenerator and recycled to the third stage of the process, may be illustrated by referring to the single drawing which describes a flow diagram of such typical procedure. For simplicity, valves, gauges, etc., not needed for an understanding of the invention, have been omitted. The drawing is hereby incorporated and made a part of the present specification.

A solid saturated aliphatic hydrocarbon such as a refined paraffin wax is charged into oxidation reactor 1 by line 2 and an oxygen-containing gas such as air by line 3. The saturated aliphatic hydrocarbon is vigorously agitated at an elevated temperature in reactor 1 for a time suflicient to obtain an oxidized product having a saponification number above about 100 and preferably between about and about 450. A catalyst such as vanadium pentoxide can be employed to facilitate oxidation in reactor 1. Volatilized lower molecular weight products produced during the air-oxidation step are removed overhead from reactor 1 and passed to condenser 4 by line 5. The condenser is preferably maintained at a temperature of about 35 F. to about 90 F. by any suitable means. Any temperature sufiicient to condense a large part of the volatilized lower molecular weight products can be employed. The condensed lower molecular weight products in condenser 4 resolve themselves into two phases, an upper organic phase comprising oxidized hydrocarbolts inclndinglower organic acids, esters and: aldehydes, and azldwer aqueous phase comprising ;formic, acetic and propionic acids, and are removed from condenserr4 by line 6. Uncondensedillowerz molecular weight products comprising excess air, nitrogen, carbon monoxide and carbondioxide are removed from condenser 4 by line 7.

The air-oxidized product is removed from reactor 1 by line 8 and passedlto solvent extractor 9, and a solvent, such as methanol, is passed to extractor 9 by line 10. The pressure in the solvent extractor is maintained at substantially atmospheric pressure. The mixture is heated in extractor 9 to permit solution of the oxidized product and then passed to cooler 11 by line 12 where itis cooled slowly to a temperatureat which a Wax-like solidcrystallizes out of solution.

The mixture of wax-like phase and soluble material is removed from cooler 11 by line 13"and passed to tank 14"wherein,is mounted rotary filter 1'51 Thewaxlike solid comprisingthe fraction having the lower saponificaa tion number is removed from solutionby filter 15 and is passed'to heated tank 16 from where itcan be recycled to air-oxidation reactor 1 by line 17. If desired, the. product in tank 16- can be passed to a still where the. solvent is taken overhead and recycled to line and the molten bottoms product is returned through line 17. to air-oxidation reactor 1 for further oxidation. In the event a normally liquid aliphatic charge is employed in place oflparafiin wax, a decantation process instead of crystallization and filtration is preferably employed.

Thefilt'rate is removed from filter 1'5by line 18' and passed to still 19, where methanol is removed 'overhead' by line 20 and recycled to line It). The methanolsoluble extract, comprising the fraction having the highersaponification number, is removed from. still 19- by line 21 and passedtonitric acid reactor 22,, and nitric. 351

acid is led to reactor 22 by line 23. The pressure in. reactor 22 is maintained at an elevated pressure. The nitric acid reactor can be, a stainless steel pressure vessel equipped with a stirrer and, in the instant embodiment, is providedwith a nitrogen oxide regenerator 24. The air-oxidizedvproduct and nitric acid are heated-in reactor; ZZ by means not shown and stirred: If desired, reactor zlican beeoperated continuously, in which ca'se acoiltype reactor or anumber of vessels-miseries can be em-:

ployed Nitrogen. oxides formed duringthe process are;

removedoverhead from reactor 22 byline 25'. and passed: tonitrogenoxide regenerator. 24. A controlled amount. of airorother oxygen-containing gas is introduced by line. 26 into regenerator 24-and,.- as noted, N203 and NO:

arerregeneratedtherein to N02 which, alongwith the."

N02 already present, is condensedtherein and recycled' by line 27. to'reactor 22. The pressure'in regenerator 24 is of the. same order as that existing: in reactor 22 and the temperature is sufficiently low, from about 80 F.- to;

about 0 F.-, preferablyfromabout 40 F. to about 28 F.,.so as toenablethe NOz-inthe-gases to condense and: be returnedrto reactor 22. N, N20 and CO2, as. well as excess oxygen-containing regenerating, gas-,.; are removed overhead fromregenerator 24- byline 23;

At. the endof. the reaction period in.-reactor. 22, the.

oxidized product, which may comprise an upper; oil-phase layer andalower nitric acidlayer, is removed from the reactor byline 29 and passed to. separator SG-wvhich is maintained at a temperature of about 100 F; toabout" 40 F., and preferably about 80 F. to about 60 The.

upper oilphase. layer, ifapresent, may amount to. about 10-percent (based on air-oxidized charge), and generally comprises a mixture of C4 t0'C1z dibasic and Cs. toCzo monobasic acids-.- Theoil-phase layer, if. present, is-

decantedand removed from separator30-by-line 31-and the nitric-acid layer; is sentto vacuum still 32 by line 33. Nitric acid is removed overhead fromvacuum still. 32 by line 34 and can bensent tov an. absorption tower where the nitric acid can be reconcentrated with fresh; N02: and air. or can be sent to a distillation. zone where it: can-be reconcentrated :byndistillation; If desired,initrid acid' soaobtained and so .reconcentrated can be recycled tozline 23-foruseinreactor 22.

The residue from vacuum; still 32, dischargedthrough line 35 tocoolerrdti,comprises:aslurry of-solidiand liquidacids. The-slurry-iscooled, preferably .toa temperature,- of about-75 F3 to about 65-:- F.,. and allowed: to-stand'in coolerx3or-fon-several :hours to permit crystallizationof some of the dibasic' acids present in the slurry. The slurry in cooler 36 is t-hen removed by line-37 and is passed to filter 3E5, whichcan be a plateand frame press. The. filtrate from: thisfiltration: step isremoved by line 39: andpassed-ztoline 40 and, after sufiicient filter. cake has formed in'filter 38,;filtration: is stopped and the. cake is: Washed with benzene from-line 41 The benzene. wash-f ings are removed from. filter 38 by line 42 andtpassed to stripper 43. Benzene'isremoved overhead from strip. per 43 and-recycledby line 44 to line 41,,andthatremain-T ing, from the, benzene washings not going overhead in line 44 is passed to line 40. The filter cake, after the benzene washings, is transferred to dryer 46 by conveyor line 47. In dryer 46, any benzene present in the filter :cake is! removed overhead. by line 48 and recycled to line 4t .by means of. line; 44.; Theresidue; fromvdryen 46Lisaremoved therefrom. by conveyor line-49 andtcome': prises; a mixture'of' aliphaticidibasic acids.

To" the filtrate. and *the'. residue remaining; from the benzene. washings in. line :40zis added. any" solvent-or; diluent which'; would have a. preferential 'attraction'v foo monoba'sic? acids, suchasdiethyl ether, ethyl-propyliether; dipropyl ether, dimethyl ether, benzene,; carbon "tetra-; chloride-,7 ethyl carbonatm; chloroform, trichloroethylene-,; etc; throughline 50, and.the=resulting solutionris-passedt upwardly intoxthebasei: of extraction; chamber 51: Wet have found diethyl ether to be especially effective :inzoun. process, and ourdiscussion; will be with: reference .-to it. Water or'a dilute aqueoussolutionaoii a mineralfacidz such ashydrochloric acid; nitric acid,'etc., is introduced" into the top of chamber 51 by line 52and-ismixedthere in: with the solution entering. from: linev 40, resulting, in: a: lower aqueous phase; and anupper ethenphase.

The. aqueousphaseisremoved 'fronrthecbase-rof chamber: 51 .by line 53 and passed to stripper: 54 .2 Wateri's: stripped: fromthe; aqueous phase-in stripper 54? and removed-overhead: by line55, While. ami'xturecomprising aliphatic (ll-J basicuacids: is removed by line56t. Water in-line 55 =-is-'; passed'toseparator 57, wherein. water is'removed by line: SSrand: any ether which: may have been.v carried by the: water is removed by line 60 and recycled .toline 50..

Theether. phase 'is-removed. overheadfrom chamber: SIby line; 61- and passed to stripper.--62,:wherein ether'r istremove'd byline: 63and recycled topline 50-1by' line 60,; and a complex mixturecomprisinghigher .dibasic acids,.: monobasic acids and.nitrogen-containingacids isremoved: by line; 64.. Ifldesired,.the.acids removedzinline fi l as well asrany. upperoil-phase layer removed from separator: 30 byline 31,..can be recycled to eitheriair oxidation raactor 1, nitric acid. reactor 22, .or both.

The'product obtained in line -49 comprisesa: mixtures ofaliphatic dibasic acidsicontaining fromabout 4 toabout- 10 carbonqatoms, predominantly acids "having. an even number of; carbon atoms, and the product obtained in, line 56comprises a mixture of aliphaticadibasicacids" con taining' about 3 to about 9 carbon. atoms 'per: molecule; 1 predominantly acids. having; anodd number. of carbons. atoms.

The. following'example shows the. large amountof nitric: acid. needed in a typical nitric acid oxidatiomprocess: for; converting parafiin hydrocarbons to diba'sic acids:-

EXAMPLE 1 100..partsz;of.:a.=132": F; melting point: refined parat-u'ii-w wax and 400 parts otll9.0x.percent:nitricacid werepla'cedi:

in; a 1 glass :flask; equipped, with: a:.-reflux "condenser? andz a stirrer: The, mixture: was heated;to75"C. and man at tained at that temperature for 30 hours. The stirrer was operated during the entire period to insure thorough mixing of the reactants. During the course of the experiment 3,150 parts of 97 percent nitric acid was added to maintain the acid concentration at 90 percent. At the end of 30 hours the reaction was complete, as shown by the disappearance of the wax phase. After removal of the nitric acid by distillation under vacuum, the product was a viscous liquid containing suspended solids. 65.8 parts of a mixture of dibasic acids was recovered from the crude product by the combination of filtration and etherwater extraction. 2,323 parts of 90 percent nitric acid was recovered from the experiment indicating a consumption of 19.9 parts of nitric acid (as 100 percent HNOa) per part of dibasic acid produced.

In order to show the substantial decrease in the consumption of nitric acid in contrast to a conventional process as disclosed above in Example 1, we have run the following typical experiment in accordance with our invention.

' EXAMPLE 2 110.2 parts of a 132 F. melting point refined parafiin wax was placed in a flask equipped with a stirrer and a condenser. The wax was heated to 160 C. and maintained at that temperature while air was blown through the molten wax. The wax was stirred vigorously throughout the reaction period of 19.5 hours. 100 parts of the air-oxidized wax having a saponification number of 232 was obtained. In addition to the air-oxidized wax, 5.7 parts of a mixture, consisting principally of formic, acetic and propionic acids, and 14.4 parts of a mixture of volatile aldehydes, esters and other oxygenated compounds, were also recovered as condensate from the exhaust air stream.

The 100 parts of air-oxidized wax was placed in a stainless steel stirred autoclave along with 500 parts of 70 percent nitric acid. A second pressure vessel was connected to the top of the autoclave in such fashion that the lower oxides of nitrogen given 011 during the reaction passed into'the second vessel, where they were regenerated with air to higher oxides which were then condensed on a cooling coil in the vessel and returned by gravity through a line to the reaction vessel. The contents of the reaction vessel were maintained at 90 C. for 30 hours. The stirrer was operated during the reaction period to insure mixing of the reactants, and air was passed through the auxiliary vesselthroughout the reaction period to reoxidize the nitrogen oxides. The products from the run were treated as in Example 1, and 53.1 parts of dibasic acids and 460 parts of 55 percent nitric acid were recovered from this experiment. sumption of nitric acid is, therefore, 1.82 parts (as 100 percent HNOs) per part of dibasic acid recovered.

A comparison of the results obtained in Example 2, run in accordance with one method of operating our invention, with those obtained in Example 1, which is typical of a conventional nitric acid oxidation process for converting paraffin hydrocarbons to dibasic acids, shows that we are able to obtain more than a tenfold reduction in the consumption of nitric acid. Thus by preoxidizing the saturated aliphatic hydrocarbons in air prior to treatment with nitric acid, the amount of oxidation necessary in the nitric acid reactor to produce dibasic acids is substantially reduced, resulting in a substantial reduction of nitric acid consumed per part of dibasic acids produced. By regenerating a portion of the nitrogen oxides to higher oxides of nitrogen and in turn converting a portion of the latter oxides of nitrogen to nitric acid, we are able to utilize the nitric acid more efficiently than if the reaction were conducted in such a way that the nitrogen oxides formed in the process were removed and The con-.

ess can be shown by comparing the results obtained in the following example with those in the previous examples.

EXAMPLE 3 100 parts of a 132 F. melting point refined paraffin wax and 500 parts of 70 percent nitric acid were charged to a rocking autoclave which was then sealed. The autoclave and contents were heated to C. and maintained at that temperature for 30 hours during which time gaseous oxygen was added. The yield of dibasic acid recovered from this experiment was 37.7 percent, and the nitric acid consumption was 2.23 parts (as percent I-INOa) per part of dibasic acid recovered.

The economy in nitric acid consumption brought about merely by regenerating and using the nitrogen oxides formed during the nitric acid reaction stage of the process is evident from comparison of the nitric acid consumptions in Examples 1 and 3. However, the yield of dibasic acids in Example 3 is relatively low and the consump: tion of nitric acid is still higher than desired in commercial operations. As shown in Example 2, improvement in yield of dibasic acids and consumption of nitric acid is obtained in the two-stage process with regeneration and use of the nitrogen oxides formed during the second stage of the process.

While Example 2 illustrates the saving in nitric acid consumption in a two-stage process in which a wax is oxidized in air to a saponification number of 232 and the air-oxidized product is subsequently oxidized with nitric acid, the following example illustrates the further reduction in nitric acid consumption obtained by extracting from the air-oxidized product a fraction having-a higher saponification number and a fraction having a lower saponification number and subjecting only the fraction having the higher saponification number to oxidation with nitric acid.

EXAMPLE 4 141 parts of 132 F. melting point refined paraffin wax was oxidized with air as in Example 2 to a saponification number of 238. 127 parts of the air-oxidized wax and 25.7 parts of condensed products (as in Ex ample 2) were recovered. The air-oxidized wax was then dissolved in 305 parts of methanol and heated to 60 C. to insure solution, and then slowly cooled to 20 C., at which temperature a wax-like solid crystallized out. The extract solution was then separated from the solid by filtration, and the methanol was removed from each phase by heating. The methanol-soluble fraction amounting to 100 parts was found to have a saponification number of 251 and the methanol-insoluble fraction amounting to 27 parts was found to have a saponification number of 139.

The 100 parts of methanol-soluble air-oxidized wax was placed in a stainless steel rocking autoclave along with 500 parts of 70 percent nitric acid. The reactor and contents were heated to 90 C. over a period of 4 hours and maintained at that temperature for 26 hours more. Gaseous oxygen was added at intervals throughout the run and after the autoclave hadbeen cooled it was opened and the reaction product consisting of an upper organic layer of liquid acidic material amounting to 5.8 parts and a lower nitric acid layer was removed. The two phases were separated by decantation and nitric acid was removed from the lower layer by vacuum distillation. The distillate residue was a near-solid mixture of viscous liquid acid and solid acids. 58.3 parts of a mixture of dibasic acids was recovered from the residue by a combination of filtration and ether-water extraction. 984 parts of 61.8 parts of nitric acid was recovered from the experiment, indicating a consumption of 088 part of nitric acid (as 100 percent nitric acid) per part of di basic acid produced.

A comparison of the nitric acid consumption values aromas in Examples 2 and 4 shows that a 51.6 percent saving in nitric acid is obtained whentheair-oxidized wax prodnot is extracted with methanol and the methanol-soluble fraction only is'subject to the nitric acid oxidation. The methanol-insoluble fraction is. not discarded but can be recycled to the air-oxidation zone.

While Example 2 illustrates the saving in. nitric acid consumption in an oxidation process in which nitrogen oxides are regenerated inan outsideregenerator and recycled to the'nitric acid reactor, the-following example illustrates the reductionobtained in'nitric acid consumption by introducing the oxygen-containing gas in the nitric acid reactor'and regenerating the nitrogen oxides therein.-

EXAMPLE 5 110.2 parts of a 132 F. melting point refined paraflin waxwas placed in a glass flask equipped with a stirrer and a reflux condenser. The waxwasheatedato 160 C. and maintained at that temperature for 12.8 hours, during. which period the. wax was stirred and air blown therethrough. 100 parts of air-oxidized wax having a saponification number of 238 was recovered. To the 100 parts of air-oxidized wax was added 500 parts of 70 percent nitric acid and the mixturecharged to a stainless steel rocking autoclave. The reactor and contents were heat-' ed to 90". C. over aperiod of 4 hours and maintained at that temperature for 26 hours more, during which time gaseous oxygen was added. The yield of dibasic acid from this experiment was 53.9 percent and the nitric acid consumption was 1.0 r parts of nitric acid (as 100 percent HNOa) per part of dibasic acid recovered.

While in Example 5 we have shown the reduction obtained in nitric acid consumption by introducing theoxy gen-containing gas in the. nitric acid reactor and regenerating the nitrogen oxides therein, where the charge consists of a refined paraflin wax, the following example illustrates a similar type of operation where the charge consists of recrystallized foots oil.

EXAMPLE 6 211 parts of foots oil obtained from sweating-of paraffin wax was dissolved in a solution comprising 90. ercent by volume of acetone and 10 percentby volume of tri chloroethylene, in the proportion of one kilogram of foots oil to 3 liters of the solvent, by heating at a temperature of about 50 C. The resulting solution was chilled to a. temperature of about C. over a period of about hours; after which it was filtered. The resulting wet cake was again dissolved in 3 liters of the same solvent by heating to about 50 C. The latter solution was chilled to a temperature of about 0 C. over a period of about 5 hours, after. which it was filtered, resulting in a wet cake comprising. recrystallized foots oil and some solvent. After drying of the wet cake a yield of 56.5 percent of recrystallized foot-s oil was obtained.

119 parts of the recrystallized foots oil so obtained was air oxidized at a temperature of about 180 C. for

about 8.5 hours to obtain 100 grams of a product having,

a saponification number of about 185. The product was placed in a stainless steel rocking autoclave with 500 parts of 70 percent nitric acid. Gaseous oxygen was introduced intermittently into the autoclave which was held at a temperature of about 90 C. for a period of about 30 hours. The yield of dibasic acids from this run was 51.6 percent and the nitric acid consumption was 1.10 parts of nitric acid (as 100 percent nitric acid) per part of dibasic acid recovered.

As shown in Examples 5 and, regeneration of nitrogen oxides in the nitric acid reactor, shows a marked reduction in nitric acid consumption over the conventional singlestage nitric acid oxidation process and, in fact, shows a reduction in the amount of nitric acid consumed overv the process set forth in Example 2 wherein regenera- "on of nitrogen oxides is conducted in a separate regentor.

5 sas onification No; of Charge to Nitric Acid While-thereduction .of-nitricacid in ,ounprocessgdeipendslztoxa large-extent: on.;thc manner inrwhicheeach of the;.-three stages thereoffiis conducted,,such-reductiomis likewise depend'entupon the extent'to-whichthe saturated aliphatichydrocarbons are oxidized in the first stage; This is show-ninthe data in; the followingrtable; The experiments reported in the table: were made-asrin Ex ample 5, and Experiment 3 in.the.tableis; in fact, Ex:- ample;5.-

T c'rble I.Effct' of'saponification number of air-oxidized wax on yield Experiment No. 1 2 i 3 4 ea 1 0 148' 238- 382 Yield of Dibasic Acids,- Percen-t oi. Chargeito Nitric'Acid'Stage 37. 7 46.9 53. 9 57. 8 Yield of Dibasic Acids; Percent of Total Product 34. 3. 50. 6 57.1 73. t Nitric Acid Consumption, Parts/Part of D1- basic Acid 2.23 1. 36 1.04 1. 22 Gaseous Oxygen Consumption, Parts/P t of Dibasic'Aci'd; 1.63' 1.20 1.01 0. 76

From these datait isevidentgthat controlled air; oxida: tion prior tonit'ri'cacid oxidationresults inimproved yields. ofid'ibasic-acids and reduced oxidant consumption. While it'is true that the air. used in the first stage of the process is part of.-the; totaloxygenemployed, the cost or difii'c'ulty of air blowing at atmospheric pressure is trivial comparedto the cost or difliculty. of oxidation with nitric acid and compressedloxygen in. a pressurized :reac-tor.

Another unexpected observation, in our process is illus: tratedi'n the data i'nTa-ble' 11.. These. data. are the results of three. runs which weremade. underthe same conditions except thatthe concentration'of-the. nitric acidin. the sec-. 0nd stage. wasvariedas. shown. Run No.2 in'this. table is Example 5 .shown. above.v

Table IZ:'-Efict of nitric acidcconcentratiomuponyield 0fdibasic acids- Experiment No: 1 2 3 Nitric=Acid Concentration, Percent; L 70 50 Yield, IPercent of- A-ir-Oxidiz'ed Wax. 60.; 5 53. 9 27. 4 Nitric Acid Consumption, Parts/Part of Dibasic Acid 1.19 1.04

thec0st or difficulty of reconcentrating nitric acid aboveabout 70*percent is out ofsproportion to a corresponding: reconcentration below about 70v percent, minimumcost is obtained with about 70-percent nitric. acid, and this is especially preferred. As previously'noted; wehave alsofound that the. amount of timenecessary tozoxidize the preoxidized material in the third-stage of the process can. be.substantiallyreduced.byconducting the third stage at increasedv temperatures. Thisyis .shown in Example 7 where the temperature in the nitric acid reaction stage is raised to about "1 10 C.

EXAMPLE 7 tained at thatternperature while air was blown throughthe molten, wax. The wax was stirred vigorously throughout. the reactionperiod of'19;5 hours; parts" of air oxidized. wax having a' sapom'fication number of "232was obtained. To 100 parts of the air oxidized wax" 1 1 in a stainless steel rocking autoclave was added 500 parts of 70 percent nitric acid. The contents of the vessel were maintained at a temperature above about 50 C. for a total of about 6 hours, of which about 2 hours were at about 110 C. Products from this run comprised 58.3 5

parts of dibasic acids. The consumption of nitric acid (as 100 percent HNOs) amounted to 1.65 parts per part of dibasic acid recovered.

Thus, it will be apparent by comparing Example 7 with the preceding examples that the amount of time 10 necessary to obtain a high yield of dibasic acids can be substantially reduced by conducting at least a portion of the third stage of the process at the higher temperatures.

Obviously, many modifications and variations of the charge stock to oxidation with an oxygen-containing gas for a time sufiicient to obtain an oxidation product having a saponiiication number above about 100, separating from said oxidation product a fraction having a saponification number higher than said oxidation product and a fraction having a saponification number lower than said oxidation product, and thereafter subjecting said fraction having a saponification number higher than said oxidation product to further oxidation at an elevated temperature of about 50 C. to about 150 C. with nitric acid having a concentration above about 50 percent for a time suflicient to obtain substantial amounts of dibasic acids while admixing with the gaseous mixture comprising nitrogen oxides formed during said nitric acid reaction stage of the process an oxygen-containing gas in amounts and for a time sufficient to regenerate said nitro- 0 gen oxides, and employing the products resulting from said regeneration in said nitric acid reaction.

2. A process for the production of dibasic acids from a charge stock consisting essentially of a saturated aliphatic hydrocarbon boiling above about 250F. and having at least eight carbon atoms comprising subjecting the charge stock to oxidation with an oxygen-containing gas for a time sutiicient to obtain an oxidation product having a saponification number above about 100, separating from said oxidation product a fraction having a saponification number higher than said oxidation product and a fraction having a saponification number lower than said oxidation product, and thereafter subjecting said fraction having a saponification number higher than said oxidation product to further oxidation at an elevated temperature of about C. to about 150 C. with nitric acid having a concentration above about 50 percent for a time suiiicient to obtain substantial amounts of dibasic acids while introducing an oxygen-containing gas into the nitric acid reaction stage of the process in amounts and for a time sufficient to regenerate nitrogen oxides formed during the nitric acid reaction, and employing the products resulting from said regeneration in said nitric acid reaction.

3. A process for the production of dibasic acids from a charge stock consisting essentially of a saturated aliphatic hydrocarbon boiling above about 250 F. and having at least eight carbon atoms comprising subjecting the charge stock to oxidation with an oxygen-containing gas for a time sutficient to obtain an oxidation product having a saponification number above about 100, separating from said oxidation product a fraction having a saponification number higher than said oxidation product and a fraction having a saponification number lower than said oxidation product, and thereafter subjecting 12 said fraction having a saponification number higher than said oxidation product to further oxidation at an elevated temperature of about 50 C. to about 150 C. with nitric acid having a concentration above about 50 percent for a time sufficient to obtain substantial amounts of dibasic acids while removing from the nitric acid reaction stage of the process a gaseous mixture comprising nitrogen oxides formed during the nitric acid reaction, passing said gaseous mixture to a regeneration zone, introducing an oxygen-containing gas into said regeneration zone to regenerate nitrogen oxides in the gaseous mixture, and recycling the products resulting from said regeneration to said nitric acid reaction.

4. A process for the production of dibasic acids from a charge stock consisting essentially of a saturated aliphatic hydrocarbon boiling above about 250 F. and having at least eight carbon atoms comprising subjecting the charge stock to oxidation with an oxygen-containing gas for a time sufi'icient to obtain an oxidation product having a saponification number above about 100, separating from said oxidation product a fraction having a saponification number higher than said oxidation product and a fraction having a saponification number lower than said oxidation product by dissolving said product in a solvent selected from the group consisting of alcohols and ketones, and thereafter subjecting the soluble portion thereof comprising the fraction having the higher saponification number at an elevated temperature of about 50 C. to about 150 C. to further oxidation with nitric acid having a concentration above about 50 percent for a time sutficient to obtain substantial amounts of dibasic acids while admixing with the gaseous mixture comprising nitrogen oxides formed during said nitric acid reaction stage of the process an oxygen-containing gas in amounts and for a time suificient to regenerate said nitrogen oxides, and employing the products resulting from said regeneration in said nitric acid reaction.

5. A process for the production of dibasic acids from petroleum waxes comprising subjecting a petroleum wax to oxidation with an oxygen-containing gas for a time sutlicient to obtain an oxidation product having a saponification number above about 100, separating from said oxidation product a fraction having a saponification number higher than said oxidation product and a fraction having a saponification number lower than said oxidation product by dissolving said oxidation product in a solvent selected from the group consisting of alcohols and ketones at a temperature of about 50 C. to about C., cooling the solution to separate a waxy phase from a solvent phase, the solvent phase comprising the fractionhaving the higher saponification number and the waxy phase comprising the fraction havingthe lower saponification number, removing the waxy phase therefrom and thereafter subjecting the fraction having the higher saponification number to further oxidation at an elevated temperature of about 50 C. to about C. with nitric acid having a concentration above about 50 percent for a time sufiicient to obtain substantial amounts of dibasic acids while admixing with the gaseous mixture comprising nitrogen oxides formed during said nitric acid reaction stage of the process an oxygen-containing gas in amounts and for a time sufficient to regenerate said nitrogen oxides, and employing the products resulting from said regeneration in said nitric acid reaction.

6. A process for the production of dibasic acids from petroleum waxes comprising subjecting a petroleum wax to oxidation with an oxygen-containing gas for a time sufficient to obtain an oxidation product having a saponification number above about 100, separating from said oxi 0 dation product a fraction having a saponification number higher than said oxidation product and a fraction having a'saponification number lower than said oxidation product by dissolving said oxidation product in methanol at a temperature of about 60 C., cooling the resulting solution to a temperature of about 20 C. for a time sutiicient to separate a waxy phase from a solvent phase, said waxy phase comprising the fraction having the lower saponification number and said solvent phase comprising the fraction having the higher saponification number, removing the waxy phase therefrom by filtering, removing methanol from said solvent phase and thereafter subjecting said latter phase free of methanol comprising the fraction having the higher saponification number to further oxidation at an elevated temperature of about 50 C. to about 150 C. with nitric acid having a concentration above about 50 percent for a time sufiicient to obtain substantial amounts of dibasic acids while admixing with the gaseous mixture comprising nitrogen oxides formed during said nitric acid reaction stage of the process an oxygen-containing gas in amounts and for a time sufiicient to regenerate said nitrogen oxides, and employing the products resulting from said regeneration in said nitric acid reaction.

7. A process for the production of dibasic acids from a charge stock consisting essentially of a saturated aliphatic hydrocarbon boiling above about 250 F. and having at least eight carbon atoms comprising subjecting the charge stock to oxidation with an oxygen-containing gas for a time suflicient to obtain an oxidation product having a saponification number above about 100, separating from said oxidation product a fraction having a saponification number higher than said oxidation product and a fraction having a saponification number lower than said oxidation product, and thereafter subjecting said fraction having a saponification number higher than said oxidation product to further oxidation at elevated temperatures of about 50 C. to about 110 C. for about 6 hours, of which about 2 hours are at about 110 C., with nitric acid having a concentration above about 50 percent for a time sutficient to obtain substantial amounts of dibasic acids while admixing with the gaseous mixture comprising nitrogen oxides formed during said nitric acid reaction stage of the process an oxygen-containing gas in amounts and for a time sutficient to regenerate said nitrogen oxides, and employing the products resulting from said regeneration in said nitric acid reaction.

8. A process for the production of dibasic acids from a charge stock consisting essentially of a saturated aliphatic hydrocarbon boiling above about 250 F. and having at least eight carbon atoms comprising subjecting the charge stock to oxidation with an oxygen-containing gas for a time sufficient to obtain an oxidation product having a saponification number above about 100, separating from said oxidation product a fraction having a saponification number higher than said oxidation product and a fraction having a saponification number lower than said oxidation product, and thereafter subjecting said fraction having a saponification number higher than said oxidation product to further oxidation at an elevated temperature of about C. to about C. with nitric acid having a concentration above about 50 percent for a time sufficient to obtain substantial amounts of dibasic acids while admixing with the gaseous mixture comprising nitrogen oxides formed during said nitric acid reaction stage of the process an oxygen-containing gas in amounts and for a time suflicient to regenerate said nitrogen oxides, and employing the products resulting from said regeneration in said nitric acid reaction; removing unrcacted nitric acid from the dibasic acid product, filtering said latter product to remove a fraction of dibasic acids and obtain a filtrate comprising a second fraction of dibasic acids, dissolving the filtrate in a low molecular weight aliphatic ether, extracting the ether solution with a solution comprising water to obtain an ether layer and an aqueous layer, and stripping water from the aqueous layer to recover said second fraction of dibasic acids.

References Cited in the file of this patent UNITED STATES PATENTS 2,118,915 Butz et al. May 31, 1938 2,158,650 Beck et al. May 16, 1939 2,190,453 King et al. Feb. 13, 1940 2,452,741 Fleming Nov. 2, 1948 2,486,454 Zellner Nov. 1, 1949 2,592,964 Smith Apr. 15, 1952 2,682,553 Kirk et al. June 29, 1954 2,729,665 Buckmann Jan. 3, 1956 

1. A PROCESS FOR THE PRODUCTION OF DIBASIC ACIDS FROM A CHARGE STOCK CONSISTING ESSENTIALLY OF A SATURATED ALIPHATIC HYDROCARBON BOILING ABOVE ABOUT 250*F. AND HAVING AT LEAST EIGHT CARBON ATOMS COMPRISING SUBJECTING THE CHARGE STOCK TO OXIDATION WITH AN AOXYGEN-CONTAINING GAS FOR A TIME SUFFICIENT TO OBTAIN AN OXIDATION PROUCT HAVING A SAPONIFICATION NUMBER AOBVE ABOUT 100, SEPARATING FROM SAID OXIDATION PRODUCTS FRACTION HAVING A SAPONIFICATION NUMBER HIGHER THAN SAID OXIDATION PRODUCT AND A FRACTION HAVING A SAPONIFICATION NUMBER LOWER THAN SAID OXIDATION PRODUCT, AND THEREAFTER SUBJECT SAID FRACTION HAVING A SAPONIFICATION NUMBER HIGHER THAN SAID OXIDATAION PRODUCT TO FURTHER OXIDATION AT AN ELEVATED TEMPERATURE OF ABOUT 250*C. TO ABOUT 150*C. WITH NITRIC ACID HAVING A CONCENTRATION AOBVE ABOUT 50 PERCENT FOR A TIME SUFFICIENT TO OBTAIN SUBSTANTIAL AMOUNTS OF DIBASIC ACIDS WHILE ADMIXING WITH THE GASEOUS MIXTURE COMPRISING NITROGEN OXIDES FORMED DURING SAID NITRIC ACID REACTION STAGE OF THE PROCESS AN OXYGEN-CONTAINING GAS IN AMOUNTS AND FOR A TIME SUFFICIENT TO REGENERATE SAID NITROGEN OXIDES, AND EMPOLYING THE PRODUCTS RESULTING FROM SAID REGENERATION IN SAID NITRIC ACID REACTION. 